The previously issued patent cross-referenced above explained the advantages of using a truncated conical inflatable diaphragm as the lifting element in an inflatable lifting device. Subsequent operating experience has proven the validity of the advantages claimed for this design.
The manufacture and use of these lifting devices has resulted in a number of innovations in the manufacture of the conical diaphragms and their mountings to adjacent structure. These improvements are described and claimed herein.
Operating experience has also demonstrated that lifting devices which employ a truncated conical diaphragm as their inflatable lifting element have a natural relationship between their transverse diametrical width and their maximum lifting height. Although the ratio of lifting height to width can be altered somewhat by changing slope of the truncated cone, precision of lifting height control decreases whenever slope of the cone is increased. These considerations effectively limit the practical lifting height available from any truncated conical diaphragm of a given transverse diameter. There are many applications for this type lifting device, however, where a greater jacking height would be desirable. This is accomplished in the present invention by effectively stacking one truncated cone on top of another to produce a "two-stage" truncated conical lifting diaphragm. This effectively doubles the jacking height available from a device of any given diameter.
One of the advantages of the type lifting device described is its low profile when deflated. This low profile results not only from the conical shape of the lifting diaphragm, but also from the flexibility of the assembled diaphragm. Normally the stronger a diaphragm is made, the greater its stiffness will be. It is a feature of this invention, however, that a multi-layer construction can be employed for the diaphragm to increase its strength without materially increasing its stiffness.
Since lifting devices of the type described are typically used to elevate massive loads, safety is a prime concern in their design. The invention described herein includes means to prevent the device from being over-pressurized at its maximum lifting height. Means are also described which prevent a loaded device from descending uncontrollably in the event the supply line for lifting fluid becomes disconnected during operation.